Re: objrmap and vmtruncate

[Martin J. Bligh]

>> I'm not convinced that we can't do something with nonlinear mappings for
>> this ... we just need to keep a list of linear areas within the nonlinear
>> vmas, and use that to do the objrmap stuff with. Dave and I talked about
>> this yesterday ... we both had different terminology, but I think the
>> same underlying fundamental concept ... I was calling them "sub-vmas"
>> for each linear region within the nonlinear space. 
> 
> that's wasted memory IMHO, if you need nonlinear, you don't want to
> waste further metadata, you only want to pin pages in the pagetables,
> the 'window' over the pagecache (incidentally shm)

Hold on a minute ... don't the rmap chains (which this would be replacing)
waste rather more space than this anyway? I'd rather have it per linear
area than per-page ... think of it as "shared rmap pte chains with offsets"
if you like ;-)

M.